<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>背景图片的奇怪现象</title>
  <style>
  body {
    margin-top: 300px;
    border: 1px solid;
    width: 3000px;
    height: 300px;
    background: url(./img/bg.jpg) no-repeat;
    background-size: 100%;
  }
  </style>
</head>
<body>
  
</body>
</html>